Apparatus and Method for Direct Patterning of an Organic Material Using an Electrostatic Mask

ABSTRACT

A deposition system that mitigates feathering in a directly deposited pattern of organic material is disclosed. Deposition systems in accordance with the present disclosure include an evaporation source, an electrically conductive shadow mask, and an electrically conductive field plate. The source imparts a negative charge on vaporized organic molecules as they are emitted toward a target substrate. The source and substrate are biased to produce an electric field having field lines that extend normally between them. The shadow mask and field plate are located between the source and substrate and each functions as an electrostatic lens that directs the charged vapor molecules toward propagation directions aligned with the field lines as the charged vapor molecules approach and pass through them. As a result, the charged vapor molecules pass through the shadow mask to the substrate along directions that are substantially normal to the substrate surface, thereby mitigating feathering in the deposited material pattern.

STATEMENT OF RELATED CASES

This case claims priority to U.S. Provisional Patent Application Ser.No. 62/492,517 filed on May 1, 2017 (Attorney Docket: 6494-220PR1),which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to material deposition in general, and,more particularly, to direct patterning of a material layer on asubstrate via deposition of the material onto the substrate through ashadow mask.

BACKGROUND

Semiconductor fabrication requires the formation of one or morepatterned layers of material on the surface of a substrate. The mostcommon approach for forming a material pattern is to deposit afull-surface layer of the material over the entire surface of thesubstrate and then remove the material everywhere except where it isdesired. This is commonly referred to as “subtractive patterning.”

Unwanted material is removed in a multi-step process in which a layer ofphotoresist is formed over the material layer and illuminated with apattern of light that is based on the desired material pattern. After ithas been exposed, the photoresist covering the unwanted material isdissolved in a strongly basic developer solution, which leaves behind aphotoresist mask that covers the material to remain on the substrate. Anetchant is then used to remove the exposed material, thus patterning thematerial pattern as desired. Afterward, the photoresist mask must beremoved and the substrate must be thoroughly cleaned to ensure noresidue of photoresist or etch product remains on any of its surfaces.

During a subtractive patterning process, everything on the substrate(i.e., any previously defined structures and materials, etc.) is exposedto harsh chemicals, including the photoresist developer solution, theetchant used to pattern the material layer, and the chemicals used toclean the substrate. Unfortunately, many materials, such as organic andbiological materials, cannot survive exposure to one or more of thesechemicals. As a result, subtractive patterning cannot be used for such“sensitive materials” or to pattern any material layer formed subsequentto deposition of a sensitive material on a substrate. For suchoperations, therefore, a direct patterning process must be used.

A direct patterning process forms a desired pattern of material as it isdeposited, thereby avoiding the need for post-deposition treatments andthe harsh chemicals they normally involve. One such direct-patterningprocess is shadow-mask deposition, which is analogous to stencil-basedprinting techniques, such as stencil painting, silk screen printing, andthe like.

A shadow mask used in semiconductor fabrication often includes a thinlayer of structural material having a pattern of apertures (i.e.,openings) that matches the pattern desired for the deposited material.During shadow-mask deposition, vapor molecules of the material isgenerated such that they flow from a source toward the substratesurface. The vapor molecules can be generated via any of a variety ofprocesses, such as thermal evaporation, sputtering, and the like. Theshadow mask is positioned just in front of (but typically not in contactwith) the substrate surface. When the flow of material reaches theshadow mask, the passage of material to the substrate is blockedeverywhere except at the apertures. As a result, the material layer isdirectly patterned during its deposition on the substrate and noadditional post-deposition processing is required.

Historically, shadow-mask deposition has been used in semiconductorfabrication to define patterns of relatively large (>50 micron)features, such as wire-bond pads, etc. A typical shadow mask used insuch applications is a thin, patterned metal layer held in an annularframe. While the minimum feature size and minimum separation betweenapertures for such shadow masks is quite large (typically greater thanseveral tens of microns), such shadow masks are perfectly suitable fordefining large-feature-size, sparse patterns of material like wire-bondpad patterns.

More recently, it has become desirable to employ shadow-mask depositionin the formation of electronic devices based on organic materials, suchas organic light-emitting diodes (OLED), active-matrix OLED displays,organic solar cells, biological-material-based sensors, and the like. Inmany cases, much higher resolution and pattern density is required thancan be achieved with a conventional metal-based shadow mask. As aresult, high-performance shadow masks based on thin dielectric orsemiconductor layers have been developed that enable feature sizes andpattern densities that are less than or equal to ten microns.

Such high-performance shadow masks typically have a very thin (<1micron) layer of structural material (e.g., silicon nitride, silicon,etc.) disposed on an annular frame formed from a semiconductor or glasshandle substrate. The apertures are formed in the thin structural layer,after which the center portion of the handle substrate is removed,leaving the central region of the structural layer as a patternededge-supported membrane.

Theoretically, during shadow-mask deposition, material deposits only onthe surface of the substrate in those regions located directly behindthe apertures. In practice, however, as the vapor of the materialtravels from the source to the shadow mask, many vapor moleculespropagate along directions that are not perfectly normal to the shadowmask and substrate. As a result, some molecules continue to travellaterally after passing through the shadow mask such that the resultantpatterned regions extend beyond the edges of the apertures. Themagnitude of this lateral spreading of the features (referred to as“feathering”) is a function of the separation distance between thesubstrate surface and the shadow mask, which is preferably very small—afew microns at most, as well as the orientation of the source relativeto the center of the shadow mask.

While feathering is not a critical issue when forming large, widelyspaced features (e.g., wire-bond pads, etc.), it can be highlyproblematic when forming small-feature, highly dense patterns. Forexample, feathering can result in electrical shorts between adjacentelectrical components, color mixing between different pixels orsub-pixels in an OLED display, and the like. In fact, feathering hasbeen a limiting factor for the minimum feature size and pattern densityattainable using shadow-mask deposition.

To improve the fidelity between the shadow-mask pattern and the materialpattern realized on a substrate, collimators have been developed in theprior art. A collimator is a relatively thick plate containing anarrangement of narrow through-holes. The through holes are designed toenable the passage of only vaporized atoms traveling along directionsthat are nearly normal to the surface of the substrate. As a result, thevaporized atoms that pass through the shadow mask apertures have littleor no lateral component to their propagation direction and, therefore,feathering is reduced. Unfortunately, the inclusion of a collimatorleads to material waste and longer process times. Furthermore, even withthe use of collimation, the problem of feathering remains severe fordeposition systems having long substrate-to-source distances.

The need for a practical direct-deposition approach suitable fordefining high-resolution material layers remains, as yet, unmet in theprior art.

SUMMARY

The present disclosure presents apparatus and methods that enable directpatterning of an organic-material layer via evaporation through a shadowmask onto a target substrate without some of the costs and disadvantagesof the prior art. Embodiments of the present invention mitigatefeathering during shadow-mask deposition by imparting an electrostaticforce on vaporized molecules traveling from an evaporation source to atarget substrate, where the force directs the vapor molecules alongpropagation directions that are substantially normal to the substrate.As a result, the vapor molecules exhibit little or no lateral spread asthey deposit on the substrate after passing through the apertures of theshadow mask.

An illustrative embodiment is a deposition system comprising a reactionchamber that encloses an evaporation source, a field plate, and a shadowmask, where the field plate and shadow mask are located between thesource and substrate.

The evaporation source is configured to impart a negative charge onvapor molecules produced by the evaporation of organic source materialduring the evaporation process itself. The source is held at electricalground, while a first voltage is applied to a segmented conductordisposed on the surface of the substrate. The first voltage potentialproduces a first electric field whose field lines are aligned with avertical axis that is substantially normal to each of the source andsubstrate.

The field plate is a conductive plate having a coarse arrangement ofopenings that enable passage of the vapor molecules through the fieldplate. The field plate is positioned just in front of the source andheld at a second voltage that is less than the first voltage. As aresult, the field plate functions as a coarse electrostatic mask whoseopenings function as large electrostatic lenses that act to focus thenegatively charged vapor molecules along directions more closely alignedwith the vertical axis.

The shadow mask is an electrically conductive membrane having anarrangement of fine apertures suitable for forming a high-densitypattern of fine features (≤10 microns) on the substrate. The shadow maskis positioned just in front of the substrate and held at a third voltagethat is between the first and second voltages. As a result, the shadowmask functions as a fine electrostatic mask comprising a plurality ofsmall electrostatic lenses that act to further focus the negativelycharged vapor molecules along directions even more closely aligned withthe vertical axis.

In operation, organic material is evaporated at the source, whichimparts a negative charge on the resultant vapor molecules. As emittedfrom the source, the vapor molecules have a wide range of propagationdirections. As the vapor molecules approach the field plate, however,their propagation paths are curved by the electrostatic lenses of thefield plate openings such that they are more closely aligned with thefield lines of the first electric field as they pass through the fieldplate and proceed toward the shadow mask.

As the vapor molecules approach the shadow mask, the apertures of theshadow mask function as a finer set of electrostatic lenses that furtherrefine the propagation directions for the charged vapor molecules. As aresult, those vapor molecules that pass through the apertures propagatesubstantially normally to the substrate surface. In other words, theyhave little or no lateral component to their propagation directions,which significantly reduces or eliminates feathering in the materialpattern defined on the substrate surface.

An embodiment of the present invention is a deposition system operativefor forming a plurality of features on a first surface of a substratethat includes a first conductor, wherein the plurality of features isarranged in a first arrangement, the deposition system comprising: asource for generating a plurality of vapor molecules of a firstmaterial, wherein the source is configured to impart a negative chargeon each vapor molecule of the plurality thereof when it is generated; ashadow mask including a plurality of apertures that is arranged in thefirst arrangement, wherein the shadow mask is electrically conductive;and a voltage source that is configured to provide: a first voltagepotential between the source and the first conductor; and a secondvoltage potential between the source and the shadow mask, wherein thesecond voltage potential is lower than the first voltage potential; anda vacuum chamber that is configured to contain the source, the shadowmask, and the substrate.

Another embodiment of the present invention is a deposition systemoperative for forming a plurality of features on a first surface of asubstrate that includes a first conductor, wherein the plurality offeatures is arranged in a first arrangement, the deposition systemcomprising: a substrate chuck for locating the substrate such that thesubstrate defines a first axis that is normal to the first surface; asource for generating a first plurality of vapor molecules of a firstorganic material, each vapor molecule of the first plurality thereofbeing emitted from the source along a propagation direction having apropagation angle relative to the first axis, and wherein the source isconfigured to impart a negative charge on each vapor molecule of thefirst plurality thereof; a shadow mask including a plurality ofapertures that is arranged in the first arrangement; a first pluralityof electrostatic lenses, wherein a first electrostatic lens of the firstplurality thereof is operative for altering the path of a first vapormolecule of a second plurality of vapor molecule such that thepropagation angle of the first vapor molecule is reduced, wherein thefirst plurality of vapor molecule includes the second plurality of vapormolecule; and a vacuum chamber that contains the substrate chuck, thesource, the shadow mask, and the first plurality of electrostaticlenses.

Yet another embodiment of the present invention is a method for forminga plurality of features on a first surface of a substrate that includesa first conductor, wherein the plurality of features is arranged in afirst arrangement, the deposition system comprising: generating a firstplurality of vapor molecule of a first organic material such that eachvapor molecule of the first plurality thereof has a negative charge,wherein each vapor molecule of the first plurality thereof is generatedsuch that it has a propagation direction that forms a propagation anglerelative to a first axis that is normal to the first surface; passingthe first plurality of vapor molecules through a first plurality ofelectrostatic lenses that are operative for reducing the propagationangle of at least one vapor molecule of the first plurality thereof; andpassing the first plurality of vapor molecules through a shadow maskcomprising a plurality of apertures that are arranged in the firstarrangement.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-B depict schematic drawings of a portion of a direct-depositionsystem having electric-field tuning capability in accordance with theprior art, with the electric-field tuning system in its disengaged andengaged states, respectively.

FIG. 2 depicts a schematic drawing of an illustrative embodiment of adirect-deposition system in accordance with the present disclosure.

FIGS. 3A-B depict an organic diode configuration with and withoutapplied bias voltage, respectively.

FIG. 3C depicts the operation of organic diode 300 when organic vapormolecules 306 carry negative charge due to attachment of an electronduring their vaporization.

FIG. 4 depicts operations of a method for directly depositing a patternof organic-material features with high fidelity in accordance with theillustrative embodiment.

FIG. 5 depicts a schematic drawing of a cross-sectional view of anelectrostatic lens in accordance with the present disclosure.

FIG. 6 depicts a schematic drawing of an alternative embodiment of adirect-deposition system in accordance with the present disclosure.

DETAILED DESCRIPTION

FIGS. 1A-B depict schematic drawings of a portion of a direct-depositionsystem having electric-field tuning capability in accordance with theprior art, with the electric-field tuning system in its disengaged andengaged states, respectively. System 100 includes source 102, shadowmask 104, electrodes 106-1 and 106-2, electron generator 108, and vacuumchambers 110-1 and 110-2. System 100 is a vertical evaporation systemhaving vertical axis A1. System 100 is analogous to direct-depositionsystems disclosed in U.S. Pat. No. 9,273,390, which is included hereinby reference.

Source 102 is a conventional evaporation source located in vacuumchamber 110-1. Source 102 is operatively coupled with organic material112 such that, when the organic material melted or sublimed within thelow-pressure atmosphere of vacuum chamber 110-1, it evaporates toproduce neutrally charged organic vapor molecules 114.

Shadow mask 104 is a plate of structural material that includes aplurality of apertures 116 whose size and arrangement are based on thedesired deposition pattern for material 112. Shadow mask 104 is held infront of surface 120 of substrate 118 (typically a glass orsemiconductor substrate) such that apertures 116 are aligned with thesites at which features of material 112 are desired. In the depictedexample, each aperture 116 has lateral dimension d, which is equal tothe desired lateral dimension of each intended patterned feature.

Electrode 106 is an electrically conductive plate comprising a pluralityof through-holes (not shown for clarity), which allows vapor moleculesto substantially freely pass from source 102 to shadow mask 104.

Electron generator 108 is an electron gun that, when engaged, emits auniform flow of electrons into conduit 132, where the electrons canattach to neutrally charged vapor molecules 114 to produce charged vapormolecules 114′ Electron generator 108, electrode 106, and source 102collectively define electric-field tuning system 122.

Each of vacuum chambers 110-1 and 110-2 is a conventional pressurevessel operative for providing a low-pressure atmosphere.

Vacuum chamber 110-1 encloses source 102 and material 112, and isfluidically coupled with electron generator 108 and chamber 110-1 viaconduit 134.

Vacuum chamber 110-2 encloses shadow mask 104, electrodes 106-1 and106-2, and substrate 118. It also includes a gas feed-through that isfluidically coupled with conduit 132 to allow charged vapor molecules114′ to pass into the region between electrode 106-1 and electrode106-2.

FIG. 1A depicts system 100 with electron generator 108 is turned off anda voltage of 0V applied to electrode 106 so no electric field isgenerated between it and source 102 (which is held at ground). In otherwords, the system is depicted with electric-field tuning system 122disengaged. In this state, the vaporized atoms collectively traveltoward shadow mask 104 along propagation directions referred to hereinas organic beams 124, which include two broad classes of beams, normalbeams 126 and divergent beams 128.

Normal beams 126 are aligned, or nearly aligned, with vertical axis A1and their vapor molecules pass virtually straight through the shadowmask to deposit on surface 120 only within the lateral extent, d, ofapertures 116.

Divergent beams 128 are not aligned with vertical axis A1, however. As aresult, their motion has a significant lateral component after they passthrough apertures 120. Divergent beams 128, therefore, deposit moleculesof material 112 on surface 120 well beyond the lateral extent of theirrespective apertures.

Without engaging electric-field tuning system 122, therefore, organicbeams 124 generate features on surface 120 whose lateral extents are d1,which is significantly larger than d. In other words, withelectric-field tuning system 122 disengaged, no reduction of feathering,as compared to other typical prior-art direct deposition systems, isachieved by system 100.

With electric-field tuning system 122 engaged, as depicted in FIG. 1B,voltage V1 is applied to electrode 106 to generate electric field 130between electrodes 106-1 and 106-2, where the electric field issubstantially aligned with vertical axis A1. In addition, electrongenerator 108 is activated and emits a stream of electrons into conduit132, where neutral vapor molecules 114 acquire these electrons andbecome charged molecules 114′. Charged molecules 114′ then enter chamber110-2 to populate the region between the electrodes.

Under the action of electric field 130, charged molecules 114′ gain adirectional motion that is more uniformly aligned with vertical axis A1.As a result, organic beams become more aligned with the vertical axisand become aligned beams 132. Aligned beams 132, therefore, have areduced lateral component after they pass through apertures 120. Thus,they produce patterned features on surface 120 whose lateral extents arenearly equal to d (i.e., the desired lateral extent). In other words,with electric-field tuning system 122 engaged, a significant reductionof feathering, as compared to other typical prior-art direct depositionsystems, is achieved by system 100.

Unfortunately, system 100 suffers from at least two drawbacks. First,the bombardment of neutral vapor molecules 114 with electrons can leadto dissociation of their organic molecules. Second, the need to providea separate electron generator adds significant cost and complexity tothe system.

It is an aspect of the present disclosure, however, that vapor moleculescan be charged or polarized without the need for an electron generatoror bombarding the vapor molecules with high-energy electron beams.Embodiments in accordance with the present disclosure exploit the factthat an evaporation source can be configured to enable injection ofelectrons from the source into the organic material while it is beingevaporated to realize organic beams comprising vapor molecules that havea negative charge. Systems in accordance with the present disclosurealso include one or more electrically biased plates located in the pathof the charged molecules, where the electrically biased plates definearrangements of electrostatic lenses that substantially align theorganic beams with the vertical axis of the system such that they arenormally incident (or nearly normally incident) on the substratesurface.

FIG. 2 depicts a schematic drawing of an illustrative embodiment of adirect-deposition system in accordance with the present disclosure.System 200 includes source 202, field plate 204, shadow mask 206,voltage source 208, and vacuum chamber 210. System 200 is a verticaldeposition system for directly patterning an organic material layer onsurface 214 of substrate 212 with high fidelity with respect to theaperture pattern of a shadow mask.

Source 202 is a two-dimensional planar source comprising a planar metalsheet that functions as a heater that is operative for evaporatingmaterial 112. Material 112 is distributed in layer form across the topsurface of the heater element such that the metal heater is in completecontact with the layer of material 112. When heated, material 112vaporizes substantially uniformly across the surface of source 202.Exemplary planar evaporation sources suitable for use in embodiments inaccordance with the present disclosure are disclosed by Tung, et al., in“OLED Fabrication by Using a Novel Planar Evaporation Technique,” Int.J. of Photoenergy, Vol. 2014(18), pp. 1-8 (2014), which is incorporatedherein by reference.

In the depicted example, source 202 is electrically connected to groundpotential via conventional voltage source 208. In some embodiments,source 202 is electrically biased at a voltage potential other thanground.

While the illustrative embodiment includes a planar source, it will beclear to one skilled in the art, after reading this Specification, howto specify, make, and use alternative embodiments that include adifferent evaporation source, such as a single crucible, a source havinga linear arrangement or two-dimensional arrangement of evaporationnozzles, and the like.

Field plate 204 is an electrically conductive plate (typicallycomprising a metal, such as stainless steel) that includes holes 216.Field plate 204 is electrically connected to voltage source 208.

In the depicted example, holes 216 occupy a large fraction of thetwo-dimensional area of field plate 204 such that field plate 204 has aporosity of less than 20%; however, other porosities can be used withoutdeparting from the scope of the present disclosure. As discussed below,the porosity of field plate 204 is selected such that holes 216 enablesubstantially unimpeded transit of negatively charged organic beams from112 to shadow mask 206 while being small enough to function aselectrostatic lenses for substantially aligning the organic beams withvertical axis A1.

Field plate 204 is located in system 200 such that it is substantiallyparallel with source 202 with a separation distance between them of s1.In the depicted example, s1 is approximately 5 mm; however, other valuesof s1 can be used without departing from the scope of the presentdisclosure. In accordance with the present disclosure, the value of s1is chosen as any value that enables field plate 204 to electricallycouple with source 202 to form electrostatic lenses 222, as discussedbelow. Typically, s1 is within the range from approximately 1 mm toapproximately 10 cm.

When field plate 204 is biased with a suitable voltage, the field plate,source 202, and organic material 112 collectively define organic diode226, which affords embodiments in accordance with the present disclosuresignificant advantage over prior-art direct-deposition systems.Specifically, the organic-diode functionality enables the metal heaterincluded in source 202 to inject electrons into organic material 112during its evaporation such that the vapor molecules generated duringevaporation carry a negative charge. This avoids the dissociation oforganic molecules that can result from bombardment of neutral vapormolecules (as is done in system 100), as well as the significant addedexpense and complexity associated with an external evaporation chamberand charge generator.

Because the mechanism taking place in organic diode 226 is quitecomplex, a discussion of the basic operating principle of an organicdiode is provided here.

Organic Diode Operating Principle

Since the planar metal sheet of source 202 is in complete contact withthe donor organic layer (i.e., material 112), electron injection fromthe metal to the organic layer occurs. The injection is based on thework function of the material of the planar metal sheet which functionsas the cathode of organic diode 226. It should be noted that, since theplanar metal sheet is heated, its material must be stable up to atemperature of approximately 500° C.

Heating of the metal sheet heater of source 202 reduces the workfunction of its metal, which promotes electron injection into material112. By virtue of heating it to a suitable temperature, the organiclayer will continuously evaporate and the vaporized molecules will carrythe charge injected by the cathode. If the molecules areelectro-negative in nature it is easy to charge the molecules negativelyby electron injection by the cathode (the planar metal sheet heater ofsource 202).

As discussed below, by virtue of their thermal energy, the charged vapormolecules travel upward and pass through openings 216 of field plate204.

The motion of the charged vapor molecules is more highly directed inembodiments disclosed herein due to application of an electric fieldbetween the target substrate (i.e., substrate 112) and source 202. Thecharged vapor molecules are polarized since they are subjected to thiselectric field. As a result, they have an intrinsic dipole moment androtate themselves initially to align themselves parallel to the field.When the negatively charged vapor molecules reach the vicinity of asurface at positive electric potential (e.g., segmented electrode 220)their motion becomes directed toward that surface such that they arenormally incident on it (i.e., their propagation direction issubstantially normal to the surface).

FIGS. 3A-B depict the motion of polarizable vapor molecules with andwithout an applied electric field, respectively. Arrangement 300includes electrodes 302 and 304 and organic vapor molecules 306, whichreside in a vacuum environment located between the electrodes.

As shown in FIG. 3A, when no voltage is applied between electrodes 302and 304, vapor molecules 306 move randomly in all directions (asindicated by the arrows) due to their thermal energy.

When D.C. voltage, Vbias, is applied between the electrodes, however,vapor molecules 306 become polarized. As a result, those vapor moleculesthat are close to the electrode 304 move toward electrode 304, whilethose vapor molecules that are close to electrode 302 move towardselectrode 302. It should be noted that the polarized vapor moleculesthat are substantially centrally located between the electrodes continueto move in random directions.

Embodiments in accordance with the present disclosure derive additionaladvantages over the prior art because, during evaporation of organicmaterial 112, the work function of the metal structure of source 202 isreduced, which promotes electron injection into the organic material.The evaporated molecules of organic beams 226 (i.e., charged vapormolecules 230), therefore, carry the negative charge injected by thesource.

FIG. 3C depicts the highly directed motion of charged vapor molecules inthe presence of an applied electric field. It should be noted thatdirectionality of the motion of vapor molecules 306 toward positiveelectrode 304 is stronger when the vapor molecules are attached withelectrons.

Returning now to the illustrative embodiment, shadow mask 206 isanalogous to shadow mask 104; however, shadow mask 206 is electricallyconductive and is electrically connected to voltage source 208. Shadowmask 206 is positioned in system 200 such that it is substantiallyparallel with surface 214 of substrate 212. In the depicted example,shadow mask 206 is a metal plate comprising apertures 218, which areanalogous to apertures 116 described above. Apertures 218 have lateraldimension d2, and an aperture spacing that gives rise to a porosity ofapproximately 40% for shadow mask 206. In some embodiments, the porosityof shadow mask 206 is other than 40%; however, it is preferable that theporosity of shadow mask 206 is higher than the porosity of field plate204. In some embodiments, shadow mask 206 is formed of a structuralmaterial that is not electrically conductive. In such embodiments, anelectrically conductive layer is disposed on at least one of its top andbottom surfaces and electrically connected to voltage source 208.

Voltage source 208 is a conventional voltage source that is operativefor providing bias voltages to source 202, field plate 204, shadow mask206, and segmented electrode 220 of substrate 212.

Substrate 212 is a single-crystal silicon wafer that includes CMOScircuitry for operation as a high-resolution full-color OLED display,such as pixel drivers, row drivers, column drivers, timing circuits,image processors and power supplies, etc. At each sub-pixel location onsubstrate 212, an electronic via of the CMOS circuitry terminates atsurface 214 as a metal stack suitable for functioning as the anode of anOLED sub-pixel element. A full-color OLED display includes an array ofpixels, each of which comprises individually addressable sub-pixels thatemit green, red, and blue light. In the depicted example, whendepositing OLED material for one of these colors, the anodes for thatcolor across all pixels of the display are electrically coupled tocollectively define segmented electrode 220 on surface 214. Substrate212 is located in system 200 such that segmented electrode 220 andshadow mask 206 are separated by distance s2. In the depicted example,s2 is equal to approximately 1 micron; however, other values of s2 canbe used without departing from the scope of the present disclosure. Inaccordance with the present disclosure, the value of s2 is chosen, inpart, to enable shadow mask 206 to electrically couple with segmentedelectrode 220 to form a plurality of electrostatic lenses 224.Typically, s2 is within the range of 1 approximately micron toapproximately 100 microns.

It should be noted that segmented electrode 220 is depicted asprojecting significantly from surface 214. In practice, the thickness ofthese structures can be neglected and the segmented electrode can beconsidered to be coplanar with surface 214.

In some embodiments, substrate 212 is a different substrate thatincludes electronic circuitry. In some embodiments, substrate 212 doesnot include electronic circuitry. In some embodiments, segmentedelectrode comprises conductive fields that comprise transparentconductive elements.

FIG. 4 depicts operations of a method for directly depositing a patternof organic-material features with high fidelity in accordance with theillustrative embodiment. Method 400 begins with operation 401, whereinvoltage source 208 provides bias voltages, V2, V3, and V4 to field plate204, shadow mask 206, and segmented electrode 220, respectively. Thebias voltages are applied to their respective electrodes such thatV4>V3>V2>0, thereby giving rise to an electric field between segmentedelectrode 220 and source 202. In the depicted example, V4 is equal to300 V, V3 is equal to 150 V, and V2 is equal to 40 V; however, othervoltages can be used for one or more of V4, V3, and V2 without departingfrom the scope of the present disclosure. Typically, V4 is within therange of approximately 100 V to approximately 400 V; V3 is within therange of approximately 50 V to approximately 200 V; and V2 is within therange of approximately 10 V to approximately 50 V.

It should be noted that the values of voltages V4, V3, and V2 and thevalues of s1 and s2 are inter-related and selected to realize depositionof features having little or no feathering.

At operation 402, source 202 evaporates organic material 112 to giverise to charged vapor molecules 230. Charged vapor molecules 230collectively define charged beams 232.

By virtue of their thermal energy, charged vapor molecules 230 travelupward and pass through openings 216 in field plate 204. Due to theelectric field between the segmented electrode and the source, chargedvapor molecules 230 become polarized. As a result, each polar vapormolecule has an intrinsic dipole moment and rotates itself initiallysuch that it is parallel to the field.

At operation 403, charged vapor molecules 230 are pre-focused at fieldplate 204. When negatively charged polar molecules are in the vicinityof a surface at positive electric potential, the charged polar moleculeswill tend to have a directed motion towards that surface. As a result,the electric field lines between source 202 and openings 216collectively define a plurality of electrostatic lenses 222, each ofwhich gives rise to focusing of charged vapor molecules 230. As aresult, those charged beams 232 that are not directed along verticalaxis A1 (referred to as off-axis charged beams) are curved towardsurface 214 as they pass toward and through electrostatic lenses 222.

At operation 404, the focus of charged vapor molecules 230 is furtherrefined at shadow mask 206. The electric field lines between segmentedelectrode 220 and apertures 218 collectively define electrostatic lenses224, each of which gives rise to further focusing of charged vapormolecules 230 as they approach shadow mask 206. As a result, thedirectionality of charged beams 232 is further refined toward verticalaxis A1 such that they are substantially normal to surface 214 as theypass through the apertures of the shadow mask.

FIG. 5 depicts a schematic drawing of a cross-sectional view of anelectrostatic lens in accordance with the present disclosure.Electrostatic lens 500 is analogous to electrostatic lens 224; however,electrostatic lens 500 includes source 202, electrode 502, and shadowmask 206. It should be noted that the operation of electrostatic lens500 is equivalent to that of system 200 without the inclusion of fieldplate 204.

Electrode 502 is analogous to segmented electrode 220; however,electrode 502 is a continuous sheet of electrically conductive materialdisposed on substrate 212.

Voltages V5 and V6 (where V6>V5) are applied to shadow mask 206 andelectrode 502, respectively, while source 202 is held at groundpotential.

When organic material 112 is evaporated by heating source 202, thecharged vapor molecules give rise to organic beams, as discussed above.

Equipotential lines 504 and flux lines 506 in the region of aperture 218collectively define an electro-static lens that focuses thecharge-carrying organic vapor molecules. The paths of the organic vaporsare curved to form directed beams 508 such that the conductive vapormolecules of the directed beams are substantially normally incident onconductor 502.

Returning now to the illustrative embodiment depicted in FIG. 2, byvirtue of the focusing action of electrostatic lenses 222 and 224,lateral motion of charged vapor molecules 230 after they pass throughapertures 218 is significant reduced or eliminated. The feathering thatwould have occurred without it is, therefore, substantially avoided andpatterned features having the desired lateral extent of d2 on surface214 are realized.

In some embodiments in accordance with the present disclosure,additional stages of beam curvature are included by adding one or moreadditional field plates between field plate 204 and shadow mask 206.

In some embodiments, beam curvature is achieved only at shadow mask 206and no field plate is included between source 202 and the shadow mask.

FIG. 6 depicts a schematic drawing of an alternative embodiment of adirect-deposition system in accordance with the present disclosure.System 600 is analogous to system 200; however, system 600 does notinclude field plate 204. As a result, system 600 includes only one setof electrostatic lenses—namely, electrostatic lenses 224. Therefore,only one stage of beam curvature is affected in system 600.

It is to be understood that the disclosure teaches just some embodimentsin accordance with the present disclosure and that many variations caneasily be devised by those skilled in the art after reading thisdisclosure and that the scope of the invention is determined by thefollowing claims.

1-16. (canceled)
 17. A method for forming a plurality of features on afirst surface of a substrate that includes a first conductor, whereinthe plurality of features is arranged in a first arrangement, thedeposition system comprising: generating a first plurality of vapormolecules of a first organic material such that each vapor molecule ofthe first plurality thereof has a negative charge, wherein each vapormolecule of the first plurality thereof is generated such that it has apropagation direction that forms a propagation angle relative to a firstaxis that is normal to the first surface; passing the first plurality ofvapor molecules through a first plurality of electrostatic lenses thatare operative for reducing the propagation angle of at least one vapormolecule of the first plurality thereof; and passing the first pluralityof vapor molecules through a shadow mask comprising a plurality ofapertures that are arranged in the first arrangement.
 18. The method ofclaim 17 wherein each electrostatic lens of the first plurality thereofis located at a different aperture of the plurality thereof.
 19. Themethod of claim 17 further comprising passing the first plurality ofvapor molecules through a second plurality of electrostatic lenses thatare operative for further reducing the propagation angle of the at leastone vapor molecule of the first plurality thereof.
 20. The method ofclaim 19 further comprising locating a field plate between a source andthe shadow mask, wherein the field plate includes a plurality of holes,and wherein each of the first plurality of electrostatic lenses islocated at a different hole of the plurality thereof, and furtherwherein each of the second plurality of electrostatic lenses is locatedat a different aperture of the plurality thereof.
 21. The method ofclaim 19 wherein the propagation angle of the at least one vapormolecule is substantially equal to zero after passing through the secondplurality of electrostatic lenses.